This application claims the benefit of German patent application DE P 10009611.5 filed Feb. 29, 2000, herein incorporated by reference.
The present invention relates to an apparatus for controlling the tension of a traveling yam in an automatic winding device, particularly such devices having stationary and displaceable yam tensioning elements in engagement with the traveling yarn for controlling the tension of the traveling yarn in proportion to an electrical coil current generated by an electrical coil via electrical current supplied by a regulating device.
German Patent Disclosure DE 37 34 471, discloses a rake tensioner device used to control the tension of yam traveling between a feed bobbin and a takeup bobbin of an automatic bobbin winder such that the increase in brake force, the tension imposed on the yarn by the rake tensioner, is reduced once the rotational speed of the takeup bobbin has reached a predetermined threshold value. The adjustable yarn tensioning elements of the rake tensioner are adjusted by an electric motor. In this kind of drive mechanism, the forward or reverse motion of the adjustable yarn tensioning elements is generated via gearing which converts the rotary motion of the motor into a linear motion.
German Patent Disclosure DE 198 58 548, which had not been published by the priority date of the present application, discloses a traversing device for delivering a yarn to a rotationally driven cross-wound bobbin, also known as a cheese, with a traversing yarn guide that is pivotable about a pivot shaft disposed perpendicular to the axis of the cheese. The end of the traversing yarn guide that guides the yam is moved back and forth by an electrical coil disposed in a magnetic field, the coil generating and controlling the motion of the traversing yarn guide for laying the yarn on a cheese.
An apparatus of the above identified type for controlling the tension of a traveling yarn is generally know, for example in German Patent Disclosure DE 43 35 089. In that construction, the yarn tension is controlled by an apparatus which can incrementally increase or decrease the yarn tension to a desired value, for instance in order to compensate for an increased unwinding tension. The apparatus for controlling the yarn tension is part of an automatic winding device. To avoid the expense that would be required if such an apparatus were used in every individual winding unit of a bobbin winder, an output signal for controlling the yarn tension is obtained from a specific spindle and other spindles of the bobbin winder are controlled on the basis of this output signal. A tensioning device, for example a rake tensioner, having a pair of cooperating comblike parts and a solenoid acts, via a rod linkage system and an eccentric element, to adjust the degree to which the combs mesh with the traveling yarn, thus adjusting the amount of the contact angle of the yarn relative to the teeth of the combs. This construction results in relatively high inertia within the moving parts and a looseness, or play, in the gears or other transmission elements. Because of the imposed inertia, such yarn tensioners tend to increase the peak values of the yarn tension and to impair the quality of the tension control.
German Patent Disclosure DE 195 44 202, discloses an apparatus for controlling the tension of yarn to a set-point value. The yarn tension control apparatus is constructed such that a rake tensioner acts as both a tensioner and a yarn tension sensor. The adjustment of the adjustable yarn tensioning elements is accomplished by an electrodynamic drive mechanism made of a plunging coil and cup magnet assembly. A holder with adjustable prong-like yarn tensioning elements is connected to a rod supported vertically by bushing bearings and oriented transverse to direction of travel of the yarn. Linear bearings have the disadvantage of being vulnerable to soiling because of the unavoidable production of dust at the work stations, especially by softeners applied to the traveling yarn. Such a system also has a relatively high mass inertia because the total mass of the plunging coil and the holder must be moved over the entire adjustment distance. This construction hinders the reaction of the yarn tensioning elements to high-frequency fluctuations in the tension of the traveling yarn, thus increasing the incident of peaks of tension in the traveling yarn which impairs the function of the apparatus.
Thus an object of the present invention is to provide an improved apparatus for controlling the tension of traveling yarn. This object is basically achieved by affixing displaceable yarn tensioning elements of a rake tensioner and an electrical coil to a common pivot lever that has no extraneous transmission components, with a corresponding increase in inertia, nor looseness, or play, in the transmission components. The torque generated by the electrical coil has a direct effect on the tension of the traveling yarn via the displaceable yarn tensioning elements. The control of the yarn tension can be accomplished without delay and without significant friction losses because the moment of inertia of the moving parts is slight, making possible rapid reaction to high-frequency changes in traveling yarn tension. Because of the fast reaction and the low inertia, the present invention is capable of self-monitoring and automatic control to a desired tension, and functions properly even if high-frequency peaks in the tension of the traveling yarn occurs. Hence, relatively high torques available for controlling the pivot lever, and a pivot lever with a short rotating distance, and a correspondingly long adjustment distance for the displaceable yarn tensioning elements, can be attained. Thus, the displaceable yam tensioning elements can be affixed to the lever arm at a relatively long distance from the pivot axis of the pivot lever, and the applicable lever arm can be correspondingly long and very light in weight The efficiency of the present invention in applying a requisite torque to the pivot lever is high, whereby the electrical coil can be disposed relatively close to the pivot axis.
A moment sufficient for effective control of the yarn tension can already be generated with an apparatus that is structurally quite small. The compact, structurally simple design requires little structural outlay which is highly advantageous in machines that have many work stations, such as spinning or bobbin winding machines. The apparatus also requires little space which is extremely desirable, given the limited space available at such work stations.
The rotatable pivot lever is supported by a rotary bearing, preferably a roller bearing and is thus supported with little friction. A rotary bearing, compared with a linear bearing, can be better sealed and is markedly less vulnerable to soiling. To further reduce the inertia of the controlling apparatus, a magnet bearing, hydraulic bearing, or air bearing can be used instead of the roller bearing. Additionally, the pivot lever can be made from very lightweight material, thus reducing the mass moment of inertia and the inertia associated with the controlling apparatus.
The above-described advantages lead individually and in combination to a marked improvement in an apparatus used to control the tension of a traveling yarn, particularly to the quality of the control.
Further details, features and advantages of the present invention will be disclosed in and understood from the following disclosure of one or more preferred embodiments of the present invention with reference to the accompanying drawings.